The present invention relates to an apparatus and method for use in channelizing telephone transmission equipment, and in particular, for providing a protocol for communication between a central processing unit and channel units.
The primary purpose of a PCM digital multiplexer system is the conversion of voice frequency signals to digital signals using standard sampling and encoding techniques and the multiplexing of 23 additional digitized samples into a T1 serial transmission format. Within the format of the T1 serial bit stream are 24 eight bit locations commonly referred to as time slots into which the encoded data can be placed. The normal approach to assigning these time slots to the individual channels has been on a fixed physical slot to time slot basis. In other words, each physical slot is identified to a particular time slot.
With the evolution of PCM carrier systems and a number of different timeslot assignment sequences, there is a requirement to provide the ability to re-assign physical slots to different timeslots within the T1 format in order to be backward compatible with the older systems.
In addition, there is a requirement to provide special conditioning of the analog portion of the circuit due to those transmission parameters which are caused by cable losses such as gain and equalization. Normally these parameters are adjusted by switches or potentiometers located on each channel unit. In order to provide a means to adjust these parameters and assign timeslots from a common database, a central processing unit must be able to communicate this information to each channel unit. The communication protocol devised for this particular application is the subject of this invention.